SEATTLE (Reuters) - Manufacturers of cannabis-infused products promoted as having health benefits for both people and pets have received warning letters their claims were untested and must be modified, the U.S. Food and Drug Administration said on Thursday.

The FDA sent letters over the past two weeks to nearly a dozen companies, including Washington-state based Canna Companion, which markets a supplement infused with hemp to dog and cat owners.

"This product is an unapproved new animal drug and your marketing of it violates the FD&C Act," the letter reads. The act gives the FDA authority to oversee safety and benefit claims of food, drugs and cosmetics.

Warning letters have also been sent to Seattle-based Canna-Pet, LLC, which makes pet treats and supplements infused with CBD, an active cannabinoid, and to California-based Hemp Oil Care, which sells cannabis-infused "products for therapeutic healthcare purposes" marketed to humans.

"The reason they got warning letters is not what is or isn't in the product," said FDA spokesman Jeff Ventura. "It's because they made therapeutic claims."

The letters require each company to remove claims on its website, packaging and marketing material that the products can improve health or prevent disease and illness.

The FDA, which says it supports research into cannabis, said scientists tested all the cannabis-laced products to ensure they did not pose a risk to public safety.

In some cases, products that claimed to owe their benefits to cannabis contained less of the compound than advertised or none at all, Ventura said.

Companies have 15 days to comply or could face enforcement consequences, according to FDA rules.

Canna Companion, based in Sultan, Washington, quickly removed therapeutic claims and testimonials from its website.

"We've been working to make sure that it's only approved language and words that will be used as to how it (the products) benefit your pet," said co-owner Lisa Anderson.

Previous language read that the capsules could "reduce cancer-associated symptoms" and "aid in decreasing severity of dementia" for dogs and cats.

She said the company's products had been tested extensively by veterinarians and that the firm did not anticipate a drop in sales because of the changes.